They’re called Great Ball Contraptions. All they do is move miniature balls from one place to another—in the most complicated manner mechanically possible. For the Lego Technic-loving designer/engineer, they’re an elite, Rube Golderberg-esque litmus test of skills.

But one epic build by ‘Akiyuky’ may have just put all others to shame. It’s 100 feet of a ball-moving assembly line, constructed over 600 hours, with each new turn representing another ingenious mechanism in moving and sorting. My personal favorite moment happens about 2:00 in, as a triad of catapults launch the balls at a basketball hoop, but only those that make it move on to the next stage.